Luminous intensity distribution

Luminous intensity is direction-dependent. It is shown in diagrams based on polar or Cartesian coordinates that are known as light distribution curves. 
The most homogeneous light distribution curve is produced by a flat surface that radiates light in a diffused pattern. Since the luminous intensity is I cos g in directions that are at an angle of g to the normal axis of the surface, the light distribution curve must be a circle. Surfaces that produce this pattern are called Lambert radiators.

	Light distribution curves of other radiators such as incandescent lamps are more uneven. The light distribution of incandescent lamps can be significantly influenced by reflectors, optical systems, prisms and so on.
Light distribution curves